1. Field of the Invention
This invention relates to stabilizing compositions which are capable of stabilizing rigid (unplasticized) halogen-containing organic polymers against the deteriorative effects of heat, light and weathering. Such stabilizing compositions comprise a mixture of an organotin mercaptide and a costabilizer which is a polyformal of a dithiodiglycol.
2. Description of the Prior Art
It has long been known that halogen-containing organic polymers, such as the commercially important polyvinyl chloride (PVC), are subject to deterioration or degradation when exposed to heat and light. Various chemical compounds and compositions have been developed to stabilize these polymers against such deterioration. For the most part, these stabilizers have been directed toward stabilization against heat, such as that encountered during processing of the polymer and its fabrication into articles. Among these heat stabilizers, some of the most effective have been the organotin mercaptide compounds.
Other organic, non-metallic compounds have also been found to be useful as heat stabilizers for halogen-containing organic polymers and are often employed as costabilizers in combination with the organotin stabilizers. For instance, U.S. Pat. No. 4,593,059 describes costabilizers which are dialkyl esters of unsaturated dicarboxylic acids.
With the increased use of halogen-containing organic polymers for rigid articles which will be exposed to light and weathering for long periods of time, e.g., housing siding and window profiles, it has become increasingly important to develop stabilizers which will not only protect the polymer against the high temperatures encountered during processing and fabrication, but will also protect the polymer against the long-term effects of light and weathering. There remains a need for improved stabilizing compositions for halogen-containing organic polymers.
The present invention is directed to a novel combination of a primary organotin mercaptide stabilizer and a costabilizer which enhances the stability of halogen-containing polymer compositions during and after processing and/or which reduces the amount of the primary stabilizer required and thereby reduces odor and tin content in the resin composition which is formed.